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Effect of onion consumption by rats on hepatic drug-metabolizing enzymes

C Teyssier1, M J Amiot, N Mondy

  • 1UMR de Toxicologie Alimentaire, INRA-Université de Bourgogne, 17 rue Sully, 21065 Dijon Cedex, France.

Food and Chemical Toxicology : an International Journal Published for the British Industrial Biological Research Association
|August 29, 2001
PubMed

Insights

Onion consumption in rats altered carcinogen-metabolizing enzymes. While it decreased activating enzyme CYP 2E1 and increased detoxifying enzymes like UDP-glucuronosyltransferase (UGT), some glutathione S-transferase (GST) subunits decreased, potentially affecting genotoxicity.

Area of Science:

  • Biochemistry
  • Toxicology
  • Nutritional Science

Background:

  • Chemically-induced carcinogenesis can be mitigated by dietary components that modulate enzymes involved in carcinogen metabolism.
  • Onions contain bioactive compounds like alk(en)yl polysulphides and flavonol glycosides, suggesting potential chemopreventive properties.

Purpose of the Study:

  • To investigate the effects of dietary onion powder on the activities and protein levels of carcinogen-activating (cytochrome P450s) and detoxifying (phase II) enzymes in rats.
  • To assess the impact of onion consumption on specific isoforms of glutathione S-transferase (GST) and UDP-glucuronosyltransferase (UGT).

Main Methods:

  • Rats were fed a diet containing 20% onion powder for 9 days.
  • Enzyme activities of cytochrome P450s (CYP 1A, 2B, 2E1, 3A), UDP-glucuronosyltransferase (UGT), and glutathione S-transferase (GST) were measured.
  • Protein levels of CYPs and specific GST subunits were determined using Western blotting.

Main Results:

  • Onion consumption induced CYP 1A and CYP 2B activities but decreased CYP 2E1 activity and protein levels.
  • Total GST activity showed a slight increase, with altered proportions of subunits: GST A1/A2 increased, while GST A3/A5 and M2 decreased.
  • UDP-glucuronosyltransferase activity (p-nitrophenol UGT) was enhanced by onion intake.

Conclusions:

  • Dietary onion modulates carcinogen metabolism by decreasing activating enzymes (CYP 2E1) and increasing detoxifying enzymes (UGT, total GST).
  • The observed decrease in specific GST subunits suggests a potential for increased genotoxic effects from certain chemicals.
  • The chemopreventive potential of onions is linked to their ability to alter the balance of carcinogen activation and detoxification pathways.

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